1. Field of the Invention
This invention relates to a data transfer system for a data entry system, and more particularly relates to a data transfer system from a keyboard to a central processing unit in the data entry system.
2. Discussion of the Prior Art
Recently, scanning type keyboards have been developed to sense "ON" and "OFF" states of key switches of the keyboard by arranging the switches in a matrix and by scanning the matrix using a central processing unit (CPU) and a LSI keyboard controller. The keyboard controller senses "ON" and OFF states of the switches during scanning of the matrix. If the keyboard controller senses an ON state of a switch, and after it confirms the ON state of the switch by means of a repeated scan, it requires an interruption to the CPU after it sets the X and Y matrix address of the switch in the ON state into its internal buffer.
FIG. 1 shows a block diagram of the prior art data entry system. The keyboard controller (KBC) 3 controls the keyboard (KB) 6 by instructions of control programs stored in a main memory unit (MMU) 4 from the CPU 2. Namely the keyboard controller 3 which is connected to the keyboard 6 is required to send an interruption such as "key-in" to the CPU 2. Therefore, the CPU 2 is occupied not only in controlling the keyboard 6 but also in occupying the main memory unit 4 to control keyboard 6 and main memory unit 4 by means of the control program and a table for code exchange stored in the memory unit 4. On the other hand, other devices controlled by the CPU are denied access to the CPU during this time. With regard to the CPU, use of the CPU is very heavy duty, and then the data entry system 1 cannot attain high processing efficiency. Also, from the physical standpoint at the connection 5 between the keyboard 6 and the keyboard controller 3, it is necessary to use a big cable to make the connection when these units are apart from each other.
Typically, the prior art data entry system employs a INTEL 8278 (or 8279) programmable keyboard interface and a Digital Equipment Corporation VT 100 full keyboard.